I played a bit with the CG API to see what languages people are using to solve solo puzzles.
This is what I found:
Data is for solo puzzles, codegolf and optim, but excluding multis and contests.
Due to API limitations data is taking into account usage of Top1000 player of the global (CodinPoints) leaderboard. (If there are some users who did lots of solo puzzles but got not much CP from multis might be missing.)
@Stilgart’s 448 Haskell solutions are at or very near the theoretical maximum.
Overall runner-up is @dwarfie with 409 PHP solutions. (Go, PHP go! No, not you, ‘GO’)
75% of top1000 players solved at least 1 solo puzzle in C++, the highest percentage.
The top1000 players solved 18.5 puzzles in Python on the average.
You can get to the virtual podium easiest in D, solving only 20 puzzles would make you #1.
Overall, the top1000 players submitted ~85k solo puzzle solutions in any language.
@Marchete submitted the most solutions, average of 36.5 per language, or 985 in total. Runner-up is dwarfie with 896.
Only 61 players bothered to submit in all the 27 supported languages. The Top1000 players used 10 languages on the average.
In Achievements: @Magus has 271/271, runners-up are @AntiSquid (267), @Di_Masta (265).
Note: I could not get info on total unique puzzle solutions per player from the API. So people using multiple languages and not solving all the puzzles they solved in their primary language might be missing from above.